There are known many types of gauging or measuring heads for the inspection of mechanical pieces in benches, transfer lines or in the so-called in-process applications in the course of the machining in machine tools.
In the known heads, the fulcrum, that couples the movable arm to a fixed support and must ensure particularly precise displacements of the arm, is achieved by either a material removal, i.e. a manufacturing process that involves delicate and costly mechanical machinings, or the arrangement, between the arm and the support, generally by removable couplings, of suitable devices for allowing arm displacements, i.e. an arrangement also requiring the utmost precision and, consequently, considerable time and costs.
In other heads, like the ones shown in U.S. Patent U.S. Pat. No. 3,946,492, an unfixed frame member carrying a feeler arm is movably coupled to a fixed base by means of a pair of spaced apart parallel leaf springs. The leaf springs allow substantially linear and parallel displacements of the feeler arm relative to the base, and render the heads unsuitable for checkings where there is shortage of room, such as in many in-process applications. Among other constructional features, the heads shown in the U.S. patent include retraction/release devices, e.g. with a bellows (FIG. 2) and a lever spring, the former being mechanically secured on one side to the fixed base and on the other side to such lever spring. The lever spring is, on its turn, pivotably connected to a fixed enclosure of the head, and cooperates with both a trasversal leg integral with the movable arm, and a biasing wire spring that also biases against such transversal leg. The dimensions and shapes of the lever and wire springs have to be precisely dimensioned so that in a non operative condition the unfixed member is retracted, whereas applying vacuum to the interior of the bellows, the action of the biasing wire spring prevails, and the unfixed member is released.